Wet Vent Bathroom Group
Wet Vent Bathroom Group
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what is the smallest vent stack i need for a sink toilet and shower
phishfood
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Under 2007 IPC, 1 1/2". Also, each attachment to a sewer or septic needs at least one 2" vent.
LiQuId
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that would be the dry portion of the vent ( above the lave flood rim ) the wet protion would need to be 2"
the shower must also come off of the 2" branch.
and every house must have at least one 3" vent. ( canadian code )
phishfood
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Once again, Liquid, we run into code differences. IPC, you can drain 1 DFU (drainage fixture unit) into an 1 1/2" wet vent. A lavatory equals 1 DFU. Minimum vent size is 1/2 the diameter of the pipe that the vent serves, but no less than 1 1/4". So, since a toilet requires a 3" pipe, the minimum vent size is 1 1/2", wet or dry. If the wet vent also serves as the drain for a tub or a shower, than it needs to be 2" minimum.
I ought to post up some pictures of the overhead drainage in the apartment complex we are plumbing right now. Keep an eye on my thread in the Project Display subforum.
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In my neck-o-the-woods, the minimum would be a 2" vent for the bathroom group if it was on the 1st floor or basement level. Toilet is 8 vent fixture units, sink is 1 f.u. and tub is 2 f.u. 1 1/2" pipe has a maximum of 10 venting fixture units and you would have 11 vent f.u. on the group.
A 3" stack vent would only be required if the bathroom group was on the 2nd floor or higher and also if there was no other 3" stack venting from the building drain in the house. If the toilet was more than 6 feet from the 3" stack vent, then an additional 2" relief vent would be required, which can be wet vented through the sink, but must continue in 2" until it terminated above the roof or connected to the stack vent.
fredunternahrer08, you may be asking what the smallest vent is, but I'm sure there is no harm in using a larger vent if possible. We also don't know what code is enforced in your area, so you may get a variety of answers.
LiQuId
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here in canada, a lav also equals 1 Dfu but the minimum size wet vent serving a W.c. is 2"
Comparison.
lav 1 Dfu
Shower 1 1/2 Dfu
W.C. 4 Dfu
even though a bathroom group is 6 1/2 Dfu's they let us call a bathroom group 6 . ( figuring that you arnt flushing the toilet using the tub AND the lav all at the same time... kinda off logic if you ask me as It happens all the time qwhen the wife is in there lol )
Caduceus, am i understanding that you have Drainage fixture units ANd venting fixture units? our code here requires that a 3" vent ( increasing to a 4" penatration at roof ) be installed in every dwelling, it is intended to provide a vent for the Sewers serving the dwellings, we must use normally open back water valves or prior to the invention of N.o. valvles you would have to install backwater valves on basement branch piping.
i will check out your thread Phishfood ...
johnjh2o
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When I was was working up north the vent had to be increased to 4" when the excited the roof. The reason being that a smaller vent would frost oven in the winter.
John
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yes, it is code here in canada that you must increase any vent by one pipe size where it exits the roof. it must be at least 6 " above the roof as well.
johnjh2o
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We had to be 10", that to is for cold winter weather it keeps the vents above snow cover.
John
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A pipe increaser at the top makes no difference in the size of the vent. Alternatively, you could put a single 4" stack through the roof - like the older plumbing codes required.
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In Michigan the roof penetration must be a minimum of 3" pipe, 12" above and below the roof. As for venting a 3pc bath, 1.5" is fine as long as it's dry. So 2" to the sink drain, and 1.5" up through the roof. I hope that makes sense.
I personally run most vents in 2", and save the 1.5" for under the cabinet use. Less complicated material list, and there's nothing wrong with a larger vent. 
On new construction I also have a habit of running 2" bathtubs too, and reducing to 1.5" at the trap. Overkill, for sure especially with smooth pvc.
Source: https://www.plumbingforums.com/threads/bathroom-venting.3180/
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